@ohplease: Because those truth seeking balls are pretty small and arent hyped to "create dimensions" or planet bust are they. Anything with that much energy doesnt just simply disperse into nothing. And it didn't say it would destroy the planet either. Just start another one of her dimensions which we dont even know the size of. Revisiting this claim over and over again is starting to get annoying. Really, if this is all it takes, then Yu Yu Hakusho characters and Prime Whitebeard who can "destroy the world" are planet busters too.
That's just perception vs. reality. Since when did the size of something determine its destructive potential though? Gudodamas are explosive, don't you know? It's been stated on-panel that Kaguya's Expansive Gudoudama (hint: Expansive) is ridiculously bigger than the normal-sized Gudoudama that Naruto, Madara, and Obito carried on them. Not really to see how they'd expand to cover the entire planet (Kakashi hinted at this seeing as he stated that if it were to continue to get bigger, then there was no way they'd be able to return to the dimension they were on).
The Gudoudama she created crumbled away because Naruto and Sasuke prevented her from completing it. Reason being that they sealed her chakra control and turned her into a gravity core for Chibaku Tensei. Thus, her control over her Gudoudama was lost, and the Gudoudama disappeared.
It didn't say it would destroy the planet, but we know that by destroying the Genesis Dimension, she would also be destroying a planet-sized object made of rock seeing as we see a moon that was stated to be of comparable size to the one on Earth being lifted from the dimensional body that they were on. And that the moon was only a small volume of the dimensional body's volume. All oft his is just visual logic.
Kaguya's dimension-busting Gudoudama statement has more precedence over Prime WB's planet busting statement, seeing as we know how it would destroy stuff (reducing to to dust) and it was specified a statement made on-panel in the manga that a new dimension would come out of it. Basically destruction and rebirth. Prime WB could be a planet buster for all we care. Not sure why YYH characters are planet busters though, seeing as they were never stated to be able to destroy the planet.
@phantomrant: Hell, we dont even know the size of that planet their on or if its even the size of Earth since it's all in some other dimension so the feat is unquantifiable really, and again all it's hyped to do is bring about a new dimension from some unknown method and it simply dispersed into nothing anyway. Not repeating this again. Especially since your main argument is the data-book that clearly loves to throw terms like lightspeed and planet-busting around.
The creation of the new dimension is part of the Gudoudama's ability to reshape the current dimension into something new, but to do that, it first reduces everything in the Genesis Dimension into nothing. It's just destruction and rebirth (don't forget Omnyoten is also a Yin-Yang ability which allows the Otsutsukis to create form out of nothing, and then breathe life into that form. There be a reason as to why Kaguya was referred to as a god-like figure). It's as simple as that.
The only thing the databook likes to throw around is the light-speed phrase. And although it's not necessarily true, it does mean that the technique is significantly faster than techniques that may not have that kind of hype. But if the databook specifies the strongest technique in the series to be an attack that can destroy and reshape a dimension, then that is a reliable author's statement (especially since it's the first time it's ever stated in the naruto databooks).